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Date:	Tue,  7 Oct 2014 16:19:42 -0700
From:	Greg Kroah-Hartman <>
Cc:	Greg Kroah-Hartman <>,, Joonsoo Kim <>,
	Vlastimil Babka <>, Mel Gorman <>,
	Rik van Riel <>,
	Andrew Morton <>,
	Linus Torvalds <>
Subject: [PATCH 3.14 25/37] mm/compaction: change the timing to check to drop the spinlock

3.14-stable review patch.  If anyone has any objections, please let me know.


From: Joonsoo Kim <>

commit be1aa03b973c7dcdc576f3503f7a60429825c35d upstream.

It is odd to drop the spinlock when we scan (SWAP_CLUSTER_MAX - 1) th
pfn page.  This may results in below situation while isolating

1. try isolate 0x0 ~ 0x200 pfn pages.
2. When low_pfn is 0x1ff, ((low_pfn+1) % SWAP_CLUSTER_MAX) == 0, so drop
   the spinlock.
3. Then, to complete isolating, retry to aquire the lock.

I think that it is better to use SWAP_CLUSTER_MAX th pfn for checking the
criteria about dropping the lock.  This has no harm 0x0 pfn, because, at
this time, locked variable would be false.

Signed-off-by: Joonsoo Kim <>
Acked-by: Vlastimil Babka <>
Cc: Mel Gorman <>
Cc: Rik van Riel <>
Signed-off-by: Andrew Morton <>
Signed-off-by: Linus Torvalds <>
Signed-off-by: Mel Gorman <>
Signed-off-by: Greg Kroah-Hartman <>

 mm/compaction.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

--- a/mm/compaction.c
+++ b/mm/compaction.c
@@ -487,7 +487,7 @@ isolate_migratepages_range(struct zone *
 	for (; low_pfn < end_pfn; low_pfn++) {
 		/* give a chance to irqs before checking need_resched() */
-		if (locked && !((low_pfn+1) % SWAP_CLUSTER_MAX)) {
+		if (locked && !(low_pfn % SWAP_CLUSTER_MAX)) {
 			if (should_release_lock(&zone->lru_lock)) {
 				spin_unlock_irqrestore(&zone->lru_lock, flags);
 				locked = false;

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